Recovery of sulphur dioxide



R. F. BACON RECOVERY 0F SULPHUR DIOXIDE Nov. 21, 1.939.

Filed May 18, 1938 2 Sheets-Sheet 1 INVENTOR l Fajmad 5 a C022 26ATTORNEYS Nov. 2l, 1939. R. FQBAoN RECOVERY OF SULPHUR DIOXIDE Filed May1S. 1938 2 Sheets-Sheet 2 Patented Nov. 21, 1939 UNITED STATES .PATENTOFFICE animes RECOVERY oF sULPHUx DIoXInE Raymond F. Bacon, Bronxvlle,N. Y. vApplication May 1s, 193s, serial No. 208,551 9 claims. (c1.26/1-11'1) This invention relates to the recovery of sulphur dioxide andhas for an object the provision of an improved method and improvedapparatus for recovering sulphur dioxide by absorption from mixtures ofgases containing sulphur dioxide. More particularly, the inventioncontemplates the provision of an improved method and improved apparatusfor employing liquid absorption media in the absorption treatment ofgases containing sulphur dioxide. A further object of the invention isto provide an improved method and improved apparatus by means of whichliquid absorption media containing solids in suspension may be employedadvantageously.

In processes for recovering sulphur dioxide from mixtures of gasescontaining the same, it is customary to subject the gases to the actionof a liquid absorption medium in a suitable absorption chamber, as, forexample, by passing the gases and the absorption medium through thechamber in counter-current ow. The pregnant absorption medium,containing the absorbed sulphur dioxide, is withdrawn from theabsorption chamber and passed to a stripping chamber in which theabsorbed sulphur dioxide is liberated, and the resulting stripped orimpoverished absorptiqn medium is returned from the stripping chamber'to the absorption chamber for re-use, the liber- 'ated sulphurdioxide-being collected and further treated, if necessary, to adapt itfor commercial use. When heat is employedl for liberating the absorbedsulphur dioxide, heat exchanging means usually are provided fortransferring heat from the stripped absorption medium to the pregnantabsorption medium passing from the absorptionchamber to the strippingchamber.

The methods and apparatus employed heretofore are quite satisfactorywhen the liquid absorption media employed are free of suspended solids,but, when the liquid absorption media contain suspended solids, forexample, in the form of suspended absorption agents or in the form ofvcompoundsprecipitated from solution' as a result of the absorptionoperation or .the stripping operation, considerable difficulty `resultsfrom clogging or chokingor from Wearing out of the pumps or otherportions of the apparatus be- Acause of abrasion. The arrangement ofapparatus employed heretofore has been such, also, that heat exchangingoperations have not been highly satisfactory.

By means of the present invention, it is possible to avoid the dicultiesencountered heretofore. In accordance with the invention, the

absorption chamber and the stripping chamber .duit through which the areso arranged relatively to one another that absorption medium may ow fromthe absorption chamber to the stripping chamber by gravity and at such arate as to inhibit or prevent the set- The interior 5 dium ows from theabsorption chamber to the stripping chamber. Such an arrangement pro-`'vides for elicient heat exchange and economical operation. Thepreferred form of apparatus of the invention comprises a substantiallyvertical tower'comprising three main elements or sections,

namely, an absorption section adjacent the top of the tower, aliberating or stripping section adja- -vcent the bottom of the tower anda heat exchange section disposed mainly between the absorption sectionand .the liberating or stripping section but having its lower portionsurrounding the walls of the stripping or liberating section.

. The invention provides an air-lift device for returning absorptionmedium from the stripping chamber to the absorption chamber. -Theairlift device preferably is operated by means of a portion of the gasto be treated by absorption. v

Such a procedure permits an increase in the eilicielncy of theabsorption operation by combin- 35 ing sulphur dioxide with liquidtransfer. In the preferred apparatus of the invention, the airliftdevice is disposed substantially centrally of the vertical tower.

The stripping chamber ofthe invention includes an open steam coil whichfunctions to heat the absorption medium for stripping and to providemake-up liquid to compensate for evaporation losses. This isparticularly advantageous when aqueous absorption media are employed and45 evaporation losses consequently are high.

One of the particular advantages of the invenv tion` resides in the factthat it permits the use of relatively highly concentrated solutions orsuspensions of absorption agents with high` ab- 50 v sorptioncapacities.. An absorption medium of the type which vmay beemployed'-advantageously in the apparatus of the invention, for example, is aconcentrated aqueous solution of a relatively highly soluble salt of arelatively slightly soluble pregnant absorption me- 15 weak acid. In theabsorption operation, the acid of the salt is regenerated .and thrownout of solution in the form of a nely divided solid. A process employingsuch an absorption medium (with excess free weak acid), invented bymeand Rocco Fanelli, is described and claimed in application Serial Number186,014, filed January 21, 1938, which application also describes andillustrates the apparatus of the present invention.

This invention will be better understood from a consideration of thefollowing description in conjunction with the accompanying drawings, inwhich Fig. 1 is an elevation of a combined absorption, liberation andheat exchanging tower of the in- Fig. 2 is a sectional elevation of theupper portion of the apparatus shown in Fig. 1;

Fig. 3 is a sectional elevation of the lower portion of the apparatusshown in Fig. 1;

Fig. 4 is "a sectional elevation of a moisture trap for removingentrained liquid from gases leaving the apparatus;

Fig. 5 is a section taken substantially along the line 5-5 of Fig. 3;and

Fig. 6 is a section taken substantially along the line 6-6 of Fig. 3.

The apparatus shown in the drawings includes a'substantially verticaltower comprising three main elements or sections, namely, an absorptionsection III adjacent the top, a liberating or stripping section Iladjacent the bottom and a heat exchange section I2 disposed mainlybetween the absorption section. I and the liberating or strippingsection II but having its lower portion surrounding the outer walls ofthe stripping or liberating section.

The heat exchange section comprises an inner vertically disposedcylinder Il and an outer cylinder I surrounding the inner cylinder anddisposed in axial alignment therewith with its inner wall spaced fromthe outer wall of the inner cylinder to form an annular passage I6 forthe ow of liquid therethrough. The outer cylinder I5 is provided at itslower end with a flange I1 which is bolted to a closure plate I8 with asuitable gasket disposed between the ange and the closure plate toprovide a iiuid tight joint. The .inner cylinder is supported adjacentits upper end by means of a substantially truste-conical closure Vmemberrigidly attached to its peripheral edge and to an airlift conduit orpipe 2l (to be described hereinafter) which extends vertically in axialalignment with the inner cylinder I l and with the frusto-conicalclosure member 20 to form fluid tight joints. The lowerend of the innercylinder Il is spaced above the bottom closure plate I6 to provide a uldpassage 22 therebetween communicating with the annular passage I6between the inner cylinder Il and the outer cylinder I5 and with theinterior 'of the liberating or stripping section II. Additional means inthe form of spaced brackets 9 extending between and attached to theinner walls of the inner and outer cylinders I3 and I5 by spot weldingand spaced supporting elements I9 disposed vbetween the lowerend'of theinnercylinder and the bottom closure plate I6 are provided for aiding insupporting the inner cylinder.

The liberating or stripping section or chamber-II is disposed in thelower end portion of the inner cylinder i4, its outer wall being formedby the lower portion of the inner cylinder, and

t its inner wall Ibeing formed by a relatively $11011;

cylinder 23 extending vertically in axial alignment with the innercylinder I I with its outer cylindrical surfaces spaced from the innersurface of the inner cylinder. The' space between the inner cylinder I4and the stripping chamber cylinder 23 is filled with a suitable heatinsulating material such as infusorial earth or' slag wool. Its lowerend is closed by means of an annular plate 24 and its upper end by theouter peripheral edge portion of an inverted frustoconical closuremember 25 having a central opening therein providing a passage for theilow of liquid between the interior stripping chamber and the interiorof the heat exchange section of the apparatus.' Both closure membersform uid tight joints between the inner cylinder I4 and the strippingchamber cylinder 23.

A closed heating coil 26 is mounted wit-hin the stripping chamber IIadjacent the bottom thereof. Steam conduits 21 and 26 extending throughthe bottom closure plate I8 are provided for introducing steam underpressure from a suitable source (not shown) into the heating coilelement 26. A conduit 30 extending through the closure plate I3 providesan outlet for the steam heating element 26. A relatively large conduit3i communicating with the interior of the stripping chamber II throughthe closure plate I8 provides means for introducing liquid into theapparatus and for draining the apparatus.V .A steam conduit 32' extendsthrough the closure plate I8 into the interior of the stripping chamberand communicates below the heating element' 26 with a transverselyextending header 33 closed at its ends, but having two or more upwardlyopening passages adjacent its ends directly below the inner and outerportions of the 'coils of the heating element 26. The conduit 32 andheader 33 provides means for introducing live steam into the absorptionsolution to aid in liberating sulphur rdioxide and to provide a portion,at least, of the make-up water required to compensate for evaporationwhen an aqueous medium is employed for absorption. This open heatingunit aids to some extent in preventing solids suspended in liquid withinthe apparatus from settling on the coils.

A downwardly opening hood 34 is mounted above the central opening in theinverted frustoconical upper closure member 25 of the stripping chamber.'I'he` hood communicates with a relatively large conduit 35 winchextends upwardly, exteriorly of the outer cylinder I5, to a pointslightly below the top of the heat exchange section I2 where it joinsand communicates with the interior of a gas separating chamber 36. Thechamber 36 extends-upwardly to a point above the lower portion of theabsorption section I0. A gas conduit 31 havinga control valve 31atherein communicates with the interior of the separating chamber 36 atthe top and with suitable gas collection apparatus (not shown).

The absorption section III comprises an outer cylinder 38 having aflanged lower end bolted to a ange mounted on the upper end portion ofthe outer cylinder l5 of the heat exchange section with a suitablegasket disposed between the flanges to provide a uid tight joint.

The cylinder 38 is flanged at the top and closed by means of a plate 39bolted to the flange with a suitable gasket betweenthe ange and plate toprovide a fluid tight joint.

The tower, comprising the absorption, heat ex- Change and strippingsections, is mounted on and spaced apart, provided with central openingsand supported within the cylinder 38.

The baille members 40 and 4I may be provided with water coolingmeans(not shown). The bailies 40 are smaller in diameter than the innerdiameter of the cylinder 38, and they are supported by the air-liftconduit 2| by attachment of the peripheral edges of their centralopenings thereto. The baiiies 4| are of the same diameter as the innerdiameterA of the cylinder 38, and they are attached at their peripheraledges to the wall of the cylinder 38. Thelower peripheral portion of thecylinder 38 is blocked off by an inverted frusto-conical ller member 54which provides a smooth upper surface inclined downwardly toward theannular heat exchanger passage I6. A

' cylindrical member 55 disposed in axial alignment with the air-liftconduit 2| functions to restrict the spraying of liquid issuing'fromthat conduit and to direct the liquid to the central portion of theupper baie 40.

The air-lift conduit 2| extends from a point adjacent to but spaced fromthe top of the cylinder 38 to a point adjacent the hood 34 where it calconduit 44. The bales 45 communicates with the interior of a conduit 42,which forms an air lift well or sump, transversely through the heatexchange section and closed at its outer ends. The air lift conduit 2|extends axially through a cylindrical casing 43, with its walls spaced`from the walls of the casing, which casing extends from a point nearbut spaced from the top of the heat exchange section to the sump 42 withwhich it communicates through a fluid tight joint. The space between theair-lift conduit 2| and the surrounding casing 43 forms an annularpassage open at the top and communicating at the bottom with theinteriorof the sump 42.

The casing 43 is surroundedby. a cylindrical conduit 44 with its wallsspaced therefrom and with its ends joined to the ends of the cylindricalconduit to f orm a sealed space forv heat insulating purposes. The spacebetween the casing 43 and the conduit 44 may be lled with a heatinsulating material such, for example, as cellite, or means (not shown)may be provided for circulating a cooling fluid such as watertherethrough. A series of baiiles 45 in the form .of connectedalternately erect and inverted frusta-conical elements formed of sheetmaterial and open at their ends are mounted on and surround thecylindriare attached to the conduit 44 adjacent the peripheral edges oftheir reduced portions to form fluid tight seals, thus providingadditional heat insulation for the casing 43. AThese baiiies provide atortuous path of travel for liquid flowing upwardly within the innercylinder I4 of the heat exchange section of the apparatus. The baiilesserve to cause desirably thorough contact of such 'liquid with the innersurface of the inner cylinder I4. 'I'he assembly comprising the baffles45, the casing 43 and the conduit 44 is supported in position by meansof brackets 49 extending between the bafes 45 and the inner cylinder I4,the brackets 49 being employed in number and size suicient to affordsuitable support for the assembly without obstructing the passagebetween the assembly and the inner cylinder.

A pipe 46 of small diameter connected with a extending supply o1 gasunder pressure (not shown) extends through the sump 42 from the exteriorof the apparatus and projects upwardly a short distance into theair-lift conduit 2|, the joints formed atl the points where the conduit46 passes through walls of the apparatus being made fluid tight. Asuitable valve 4'I is provided for controlling the ow of gasthrough theconduit 46. The source of gas to which the conduit 46 is connected mayconsist of gas containing sulphur dioxide from the same source as thatof the gas undergoing treatment in the process for the recovery of itssulphur dioxide content.

A conduit 48 is provided for introducing gases containing sulphurdioxide into the lower portion of thev absorption section. A conduit 50having atrap disposed therein is provided for conducting `gases from theabsorption section. A conduit 52 communicates with the bottom of thetrap 5| and with the annular space |6 of the heat exchange section toreturn tothe system liquid separated from the exit gases. The trap 5|comprises a chamber provided with a series of baiiles 53 disposed in thepath of travel of gases therethrough to remove from the gases liquidparticles suspended therein by reduction of velocity through change ofdirection.

Thermometer or pyrometer wells, indicated by the letter T, and conduitsand valves to permit sampling, indicated by the letter S, are disposedat suitable points in the apparatus to aid in controllingy the operation`of the apparatus.

It is to be understood that the apparatus is provided with all valvesand other control elements necessary for its successful operation andthat all joints are fluid tight where necessary. Gaskets employed may beformed of rubber, and valves may be formed of hard rubber or othersuitable corrosion resistant material. All structural elements of theapparatus which contact the absorption solution vor mixture are formedof a suitable corrosion resistant material such as 18-8 stainless steel.'Ihe nature of the apparatus is such that relatively thin and lightsheet steel may be used in-its construction. All inner surfaces aresmooth and the surfaces above the base are disposed either vertically orat relatively large angles to the horizontal to prevent localaccumulations of solids which may be suspended in the absorption medium.

Operation of the apparatus will be described hereinafter with particularreference to the use of a water solution of borax and boric acid forabsorption oi" sulphur dioxide, as described in the aforementionedapplication.

In the operation of the apparatus, a solution of borax and boric acid inwater, preferably saturated with respect to both compounds at itsboiling temperature, is introduced at its boiling temperature throughthe bottom inlet 3| in an amount sufficient to fill the apparatus to adepth slightly greater than that indicated by the liquid.

level lines shown in the lower portions of the absorber section I0 andthe gas separating chamber 36. The amount or volume of solutionintroduced should be sufficient to maintain a depth substantially equalto that indicated by the liquid level lines when the apparatus is inoperation. When the desired amount of solution hasinthe conduit 35 andgas separating chamber 3,6.

The temperature of the solution remaining in the liberation or strippingsection after the desired amount of solution has been introduced ismaintained by introducing steam under proper pressure into the heatingcoil, steam being introduced into the liquid through the header 33 onlywhen such introduction will not cause undesirable dilutionr of thesolution. Some steam can be introduced into the solution through theheader 33`constantly during the operation of the apparatus, the rate ofintroduction being determined by the rate of loss of water from thesolution by evaporation and otherwise.

Before starting the operation of the apparatus, the solution in theupper portion of the apparatus may be permitted to cool to a desirableabsorption temperature, say to a temperature of about 50 C., oroperation may be started immediately and temperature conditions allowedto adjust themselves during controlled operation.

Operation of the apparatus is started by introducing gas under pressure,preferably a portion of the sulphur dioxide-bearing gas to be treated,into the air-lift conduit 2| through the small conduit or injector tube46 extending into the air-lift conduit 2|. When the gas under pres-`sure is thus introduced, solution iiows upwardly to the top of theabsorption section I0 and downwardly therefromv to the lower portion ofthe absorption section, over the baffles 40 and 4| and into the annularpassage I6 between the inner and outer cylinders I4 and |5 of the heatexchanger section. When flow of solution through the absorber sectionhas been established, gas to be treated for the recovery of sulphurdioxide contained therein is introduced into the lowerportion of theabsorber sectionv through the gas inlet conduit 48, the gas thusintroduced passing upwardly through the absorber counter-currently tothe flow of solution.

The solution follows a tortuous path over the bailles 40 and 4| in theform of thin films of very large area. The'ascending gases follow a.similar path in reverse direction and in a state of great turbulencewhich results in thorough and intimate contact of the gases andsolution.

The sulphur dioxide contained in the gases is absorbed by the solution,and the residual gases pass to waste through the exit conduit 50 and thebaille chamber 5|.

Precipitation of boric acid which may result from the absorptionreactions does not interfere with the iiow of gas and solution or withth`e operation of the apparatus in other respects. The precipitatedmaterial will exist in the form of very finely divided particles leavinga tendency to remain in suspension, and the inner surfaces above thebase with which solution which might contain suspended matter comes intocontact are disposed at such angles that the degree of quiescencerequired to permit settling out can not be established. Y

Pregnant solution containing the absorbed sulphur dioxide iiowsdownwardly from the lower portion of the absorber through the annularpassage I6 and through the passage 22 into the lower portion of theliberating or stripping section |I. The pregnant solution is heated toits boiling point in the liberator or stripper by introducing steam at asuitable/ temperature into the heating coil 26 and header 33. Thesulphur dioxide contained in the pregnant. solution is stripped orliberated rapidly from the solution and passes upwardly through thestripper to enters the stripper in suspension in the pregnant solutiondissolves with regeneration of the berate. The solution in the stripperremains saturated with boric acid as it was when introduced into theapparatus originally.

The stripped solution passes upwardly through: l the central opening inthe closure member 25I and to the top of the heat exchanger sectionwhere it enters the annular passage surrounding the air-lift conduit 2|and flows to the air.

lift sump 42 in condition and position to be recirculated through theapparatus,

In passing upwar ly through the heat exchanger section, the strippedsolution passes in heat exchange relationship with the relatively coolpregnant solution flowing downwardly through the annular passage I6,heat being transferred readily through the thin steel wall of the innercylinder I4. Thus, the hot stripped vsolution functions to heat therelatively cool pregnant solution to a temperature approaching thesuitable stripping temperature, and the relatively cool pregnantsolution functions to extract heat from the stripped solution and coolit to a temperature suitable for absorption. It is advisable to socontrol temperatures and rates of iiow that the temperature of thepregnant solution remains below C. until it passes ,into the stripper.

Temperature control will be Aaided by using fluid cooled baffles in theabsorber, by passing or circulating a cooling uid through the closedannular insulating space surrounding the airlift conduit 2| and byregulating the heat passing to the atmosphere from the absorber and theheatv` exchanger through the use of heating means or heat dissipatingmeans.

As the stripped solution is cooled in passing upwardly through the heatexchanger, boric acid precipitates from the solution. The precipitatedboric acid is in the form of finely divided particles which tend toremain in suspension and travel through the heat exchanger and throughthe air-lift apparatus to the absorber with the true solution. Anytendency of these particles to separate and settle out is counter-actedby the dissolving action` of the hot solution in the stripper. Inoperation, conditions withinthe apparatus adjust themselves to establishand maintain suitable equilibria between liquids and solids in thevarious parts' of the apparatus.

1. Apparatus for use in the absorption treatment of a gas containingsulphur dioxide with a liquid absorption medium of vsuch character thata finely divided solid becomes precipitated )therein during the cycle ofabsorption and release of sulphur dioxide, -comprising -an absorptionchamber, a stripping chamber disposed at an elevation lower than theelevation of the ab-` sorption chamber, means for introducing a liquidabsorption medium into the absorption chamber, means for contacting thegas to be treated by absorption with liquid absorption medium within theabsorption chamber, conduit means connecting the interior of theabsorption chamber with the interior of 'the stripping chamber permttingthe flow of absorption medium from the absorption chamber to thestripping chamber by gravity, said conduit means being sufficientlysteeply inclined and free of obstructions to enable gravity ow of theabsorption medium with :finely divided solids dispersed therein without,local accumulation of such solids in said conduit, whereby said conduitmeans may accommodate iiow of absorption medium therethrough-Withoutclogging due to accumulation of solids, means for stripping orliberating absorbed sulphur di- 'oxide stripping chamber, means forcollecting sulphur dioxide liberated in the stripping chamber, and

means for returning absorption medium afterl liberation of absorbedsulphur dioxide from the stripping chamber to the absorption chamber,said returning means being suiiiciently free of constrictions andpockets to enable return of the goabsorption medium with nely dividedsolids therein without local accumulation of said solids in saidreturning means, Wherebysaid absorption medium may be returned to saidabsorption chamber without clogging of the returning means byaccumulation of solids therein.

l2. Apparatus for use inthe absorption treatment of a gas containingsulphur dioxide with a liquid absorption medium of such character that afinely divided solid becomes precipitated therein during the cycle ofabsorption and reliquid absorption medium into the absorption liftdevice by accumulation of solids therein.

3. Apparatus for use in the absorption treatment of a gas containingsulphur dioxide with a. liquid absorption medium to absorb sulphur fromabsorption medium within the" with liquid absorption medium within. 'theabsorption chamber, conduit means connecting the interior ofl theabsorption chamber with the interior of the stripping chamberpermittingthe flow of absorption medium from the absorption 5 chamber tothe stripping chamber by gravity, means for stripping or liberatingabsorbed sulphur dioxide from absorption medium within the strippingchamber, means for collecting sulphur dioxide l liberated in thestripping chamber, 10 means including an air-lift device for returningabsorption medium after liberation of absorbed sulphur dioxide from thestripping chamber to the absorption chamber, and means for utilizing aportion of the gas to be treated for operating 15 v the air-lift device.

4. Apparatus for use in the absorption treatment of a gas containingsulphur dioxide with uid absorption medium to absorb sulphur dioxide,comprising an absorption chamber, a 2( flow of absorption medium fromthe absorption 30 chamber to the stripping chamber by gravity, meansincluding a closed steam conduit Within the stripping chamber forheating absorption `medium to liberate or strip .absorbed sulphurdioxide therefrom, an open steam conduit within 3l the stripping chamberfor aiding in heating'absorption medium andv for providing make-upliquid to compensate for evaporation losses, and means for collectingsulphur dioxide liberated in the stripping chamber. 40

5. Apparatus for use in the absorption treatment of a gas containingsulphur dioxide with a liquid absorption medium to absorb sulphurdilower than lthe elevation of the absorption chamber, means forintroducing a liquid absorption medium into the absorption chamber,means for i contacting the gas to be treated by absorption with liquidabsorption medium within the absorption chamber, conduit meansconnecting `the l sulphur dioxide in heat exchange relationship withabsorption medium owing from the absorption chamber to the strippingchamber, means for returning absorption medium to'the absorption chamberafter liberation of the absorbed sulphur dioxide, and means forcollecting sulphur. dioxide liberated in the stripping chamber.

6. Apparatus' for usein the absorption treatment o'f a gas containingsulphur dioxide with 76 a liquid absorption medium of such characterthat a finely divided solid becomes .precipitated therein during thecycle of absorption and release of sulphur dioxide, comprising anabsorption chamber, a stripping chamber disposed at an elevation lowerthan the elevation of the absorption chamber, means for introducing aliquid absorption medium into the absorption chamber, means forcontacting the gas to be treated by absorption with the absorptionmedium within the absorption chamber, conduit means for conductingpregnant absorption medium from the ab'sorption chamber to the strippingchamber, said conduit means being sufliciently steeply inclined and freeof obstructions to enable gravity ow of the absorption medium withiinely divided solids dispersed therein without local accumulation ofsuch solids in said conduit, whereby said conduit means may accommodateflow of absorption medium therethrough without clogging due toaccumulation of solids, and means including an air-lift device forreturning stripped absorption medium from the stripping chamber to theabsorption chamber, said air-lift device being sufciently free ofconstrictions and suflciently steeply inclined to enable return of theabsorption medium with nely divided solids therein without localaccumulation oi such solids in said air-lift device, whereby saidabsorption medium may be returned to said absorption chamber withoutclogging of the air-lift device by accumulation of solids therein.

'7.'Apparatus for use in the absorption treatment of a gas containingsulphur dioxide with a liquid absorption medium to absorb sulphurdioxide, comprising an absorption chamber, a

' stripping chamber disposed at an elevation lower than the elevation ofthe absorption chamber, means for introducing a liquid absorption mediuminto the absorption chamber, means for contacting the gas to be treatedby absorption with the absorption medium` within the absorption chamber,means for conducting pregnant absorption medium from the absorptionchamber to the stripping chamber, means including an air-lift device forreturning stripped absorption medium from the stripping chamber to theabsorption chamber, and means for utilizing a portion of the gas to betreated for operating the air-lift device.

8. Apparatus for use in the absorption treat- I absorption and strippingchambers, and an airlift device extending through the interior of saidinner conduit from a point adjacent the stripping chamber to a point inthe upper portion of the absorption chamber.

9. Apparatus for use in the absorption treatment of a gas comprising anabsorption'chamber, a stripping chamber disposed below the absorptionchamber, an outer substantially vertical conduit connecting the.stripping chamber and the absorption chamber, an inner substantiallytvertical conduit mounted within the outer conduit, the walls of saidconduits being spaced apart to provide a substantially vertical annularpassage providing for communication between the interior of theabsorption chamber and the interior of the stripping chamber, and anair-v lift device extending through the interior of sai'd inner conduitand comprising an air-lift riser extending from a point within saidinner conduit to a point in the upper portion of the absorption chamber,and means having a liquid inlet adjacent the upper portion of said innerconduit for admitting liquid to said air-lift riser.

RAYMOND F. BACON.

